Drugs target serotonin to reduce depression and other mood disorders. Could probiotics do the same, given that the microbiome is one smooth operator in gut-brain signaling?[i]
Researchers Caroline J. K. Wallace and Roumen Milev of Queens University in Ontario asked the same in “The effects of probiotics on depressive symptoms in humans: a systematic review” which appeared in Annals of General Psychiatry in February, 2017.
The authors’ review of pre-clinical data reveals robust evidence in tested rodents:
- Chronic stress hormones reduced
- Brain-derived neurotrophic factor (BDNF), crucial for brain plasticity, memory, and neuronal health increased
- Increased tryptophan (serotonin precursor) levels
- Reduced inflammatory biomarkers
- Improved antioxidant abilities
- Behavioral changes: improved memory and reduced anxiety and depressive symptoms.
And in Humans:
The authors searched 5 databases to glean 10 total studies assessing mood symptoms, anxiety symptoms or cognition. The most frequently used probiotic strain was Lactobacillus casei, and duration of treatment period ranged from 3 weeks to 6 months.
- Mood: Of the 5 studies assessing mood, 3 reported improvement with probiotic treatment.
- Stress and anxiety: 5 of 7 relevant studies reported improvement.
- Cognition: All 3 relevant studies showed some improvement in coping and memory skills but results were conflicting.
Thus, most found encouraging results however the strain of probiotic, dosing, and duration of treatment varied widely.
How probiotics may work
Probiotics may affect mood and cognition, evidence suggests, by:
- Reducing toxic leakage into the blood thereby reducing inflammation, which shows biomarkers aligning with depression.
- Increasing production of tryptophan which converts to serotonin, a prime actor implicated in stress and emotions across the gut-brain axis.
Taken together, the findings from the included studies demonstrate that it is likely that daily consumption of a probiotic supplement could have a positive effect in improving the mood, anxiety, and cognitive symptoms present in MDD (Major Depressive Disorder).
However, the authors recommend that more uniform studies be undertaken; also suggested is creation of a clearer model for defining the numerous types of depression including major depressive disorder, bipolar disorder, seasonal affective disorder, dysthymia, and postpartum depression.
Probiotics should not be confused with 2 new terms introduced in the literature:
Encephalobiotics: includes probiotics, prebiotics, postbiotics, microbes, microbial parts, and/or agents that influence the microbiome for cognition, mental well-being, and brain health.
Psychobiotics: live organisms that, when ingested in adequate amounts, produce a health benefit in patients suffering from psychiatric illness.
[i] “… in the last decade, neurogastroenterology research has revealed extensive and direct biochemical signaling between the gastrointestinal (GI) tract and the central nervous system, referred to as the “gut–brain axis. This communication network is bidirectional and occurs via the autonomic nervous system, the enteric nervous system, the neuroendocrine system, and the immune system. This is further corroborated by the high rate of comorbidity between psychiatric disorders and GI disorders.”
Pertinent articles published previously on IPA site: